A push-to-talk (PTT) service provides direct one-to-one and/or one-to-many audio communication. PTT may include a mechanism that provides instantaneous communication between parties, and that utilizes a button to switch user equipment (UE) from a voice transmission mode to a voice reception mode. The operation of UEs in this manner may be similar to how walkie talkies operate. A PTT service may switch a UE from a full duplex mode, where both parties may hear each other simultaneously, to a half duplex mode, where a single party may speak at one time. Multiple parties to a conversation may also be included. Availabilities of parties may be checked before a call with the help of a presence function.
In the Third Generation Partnership Project (3GPP), the fourth generation (4G) cellular network includes an evolved packet system (EPS). The EPS may include a radio access network (e referred to as long term evolution (LTE) network), a wireless core network (e.g., referred to as an evolved packet core (EPC) network), an Internet protocol (IP) multimedia subsystem (IMS) network, and a packet data network (PDN). The LTE network is often called an evolved universal terrestrial radio access network (E-UTRAN). The EPC network is an all-IP packet-switched core network that supports high-speed wireless and wireline broadband access technologies. The EPC network allows UEs to access various services by connecting to the LTE network, an evolved high rate packet data (eHRPD) radio access network (RAN), and/or a wireless local area network (WLAN) RAN. The IMS network may include an architectural framework or network (e.g., a telecommunications network) for delivering IP multimedia services. The PDN may include a communications network that is based on packet switching.